Katz's Corner Episode 24: Pass Labs HPA-1 Headphone Amplifier

Nelson Pass's Lab has produced an impeccable headphone amplifier with more than enough power, that's quiet, solid, and very clean. Several other reviewers have reflected on this excellent amplifier, but I want to weigh in with my unique sonic perspective and also measurements of its performance.

Fig 2: Pass HPA-1 amplifier, rear panel

The Pass's sculpted front panel is very pretty and makes a distinctive show piece; there's no need to hide this baby. The rest of the case consists of rectangular brushed aluminum panels. Its large, weighted volume control is unique in my experiencerotational feel is more solid than any other rotary control I've ever used. It's also very precise, as I measured nearly perfect channel matching, zero error (level difference) at full gain, 0.06dB error at 3 o'clock and 0.25dB error at 12 o'clock. Jam Somasundram, its designer, has made a very wise decision, to set the voltage gain to the absolute minimum to be compatible with any current headphone and DAC source. It's specified as only 6dB though I measured 7.6dB gain into 20 Ohms at 1kHz. Even with the volume control all the way to the top, there is no noise to be heard with the most sensitive headphones.

He has implemented an unbalanced circuit, with two selectable stereo RCA inputs and a locking 1/4" TRS jack, yet it delivers plenty of power, demonstrating that it is not necessary to have a balanced output to produce superior performance. An unbalanced amp needs a higher voltage power supply than a balanced amp with the same specificationhowever, the tradeoff is that fully-balanced requires double the components and an expensive, high precision 4-gang volume control. Balanced is strictly a designer's choice, not demonstrably superior (or inferior) to unbalancedif the designers optimize the characteristics of each design. Ironically, most times Nelson Pass has advocated a fully-symmetrical approach in his products, but not in this headphone amplifier, which has a clean, minimalist design and few active components to pass the signal through.

Yes, balanced inputs may improve hum performance when very long connections are used, but that is not the case in most consumer's homes. Balanced outputs for headphones are absolutely not necessary, and even the use of the term is questionableI prefer to say "push-pull" because headphones are floating, they do not have a ground reference. The amplifier also has line level outputs, available at the press of the "preamp" switch. The line-level preamplifier comes direct from the headphone circuit with the addition of a premium coupling capacitor. I did not listen to the preamp output but I did test its functionality. Pass's technical support engineer Kent English points out "One of the goals was to enable 'not yet audiophiles', allowing them to hear their own music better than they have heard it before....for the first time. In other words build something that appeals to the music lover first, number chasers second."

Jam, who is a very enthusiastic engineer, gave me some insight on the design: The HPA-1 was designed as a small power amp, requiring an oversized power transformer and a +/-24 Volt DC supply, while most headphone amps suffice with only +/- 15 volts. The low feedback, wide bandwidth amp has J-FET inputs and a direct-coupled MOSFET output stage, fully biased in Class A throughout. But unlike a loudspeaker amp a headphone amp has to meet a huge bunch of conflicting requirements. It has to drive a wide range of loads, from very sensitive headphones with as low as 15 Ohm impedance that require high current, to insensitive headphones with impedance as high as 600 Ohms that require high voltage drive. So after a certain point design choices become subjective, deciding the least compromise in each area to ensure low noise, low distortion, wide bandwidth and good sound.

For example, there is a balancing act between negative feedback and open loop gain as too much feedback results in a shallow midrange. There are no integrated circuits in the signal path. The power supply regulator is discrete, which Jam says sounds better than an integrated circuit. It took a full year to perfect the design, which included choice of components by listening. Eliminating unnecessary components was a conscious part of the design, and with its optimized gain and imperceptible noise, Pass has avoided the need for complex gain-set switches, that can introduce noise or distortion if not set properly.

Measurements

I made some basic measurements to confirm performance. Voltage gain (unloaded) to either the preamp or the headphone output was 8.25/8.28dB at 1kHz. Loaded by 20 Ohms, the output dropped by 0.62/0.54dB, indicating an output impedance of 1.45 Ohms (left channel) at 1kHz, close to its specification of "less than 2 Ohms". This moderate output impedance indicates that high negative feedback was not a design goal, so to obtain good linearity the designer had to begin with a very linear open-loop circuit.

With a 1kHz tone, 0dBu output into 110 Ohms (5.5mW) produces nearly all 2nd harmonic, at a level of -90/-90dBu, or 0.003% THD. We can see a trace of 3rd and 4th harmonic peeking above the noise floor in the left channel only, but at insignificant level. The rest is noise and hum (See Fig. 3). Keep in mind that second harmonic is the most innocuous and "invisible" harmonic inasmuch as it is exactly one octave above the fundamental. Besides, a level as significant as 0dBu would yield a ridiculously loud 101.72dB SPL in the Audeze LCD-4 headphones (according to manufacturer's specification). The very low second harmonic is at an inaudible 11.72dB SPL! The absence of other harmonics is a testament to the very linear design and promise of good sonics.

There are also visible hum-related products near the noise floor, at a higher level than I've seen in some other headphone amplifiers. Nevertheless, this hum is inaudible with any headphone I own. The noise floor measured -95.63/-95.77dBu unweighted, 10-20kHz, so it is also inaudible. I measured an acceptable crosstalk figure (110 Ohm load) of -70dB (in either direction) throughout the majority of the spectrum, rising to -55 at 20kHz. An IM test, 19/20kHz at a total of 0dBu into 110 Ohms produced a 1kHz difference tone at a very low-105dBu and supersonic sums circa 40kHz at -75dBu, which represents very good performance (fig 4). The rise in noise floor above 40kHz is due to my Prism interface's noise-shaped converter.

For frequency response, I can measure up to about 80kHz, and within that bandwidth, I measured the Pass's response (unloaded) as ruler flat from 10 Hz (where I began measuring) and slowly rolling off to -2.25/-2.5 at 80kHz at 0dBu output.

Fig. 3: Pass HPA-1 THD at 1kHz and noise

Fig 4: Pass HPA-1 IM distortion

While attempting to measure maximum power output I ran into the first "limitation" of the HPA-1's low gain: I could not drive the amplifier into clipping with the Prism Callia's unbalanced outputs, whose maximum level at full scale is 2V RMS (+8.23dBu), the same maximum output level as a consumer CD player. The reason I put the word "limitation" in quotes is that the Callia's unbalanced outputs at full scale can drive the HPA-1 to a very healthy 15.96/15.99dBu (1.18 watts) into 20 Ohms at 1kHz, yielding 0.1% THD and which would produce a deafening 127.8dB SPL at full scale even with the insensitive Audeze LCD-4. Not an advisable condition, so the Pass's low gain is not a limitation at all. If you insist on driving your eardrums into submission you'll need a DAC or preamp with a higher level output. You could also get 6dB more level with a balanced to unbalanced adapter. Not advised!

Nevertheless, I persisted. I switched to an interface with higher output level, the Prism Lyra, so finally I can confirm that the Pass clips, with 1.07/0.7% THD at 1kHz, +21.28/+21.30dBu (4 watts) into 20 Ohms, 1/2 a watt higher than the specification. For the record, that is equivalent to an even more deafening 133dB SPL (LCD-4) which would certainly damage headphones as well as ears in continuous testing. This is a measure of what the amplifier can deliver on peaks, so if we subtract a nominal 20dB, it would satisfy some mythical listener with mezzo-forte passages of 113dB! Fogedabodit.

The Listening
I warmed up the unit for several days. The sound definitely improves throughout the first day, and I swear even after the seventh day of continuous power it keeps on sounding better. Pass advocates leaving the power on 24/7. I decided to pit the sound of the HPA-1 against the Mjolnir Pure Bipolar as a reference that I'm familiar with. I matched the gain of the Mjolnir (balanced) and the Pass (unbalanced) within 0.1dB at 1kHz into a 110 Ohm load. The Pass volume control was set to full level and the Mjolnir ended up at about 3 o'clock. I built a high quality TRS male to XLR 4 pin female adapter so I could quickly exchange balanced headphones between the two amps.

I used JRiver Media Center on PC to play high resolution files into the Prism Callia DAC via AES/EBU from my Lynx interface. JRiver fed Acourate Convolver via Acourate ASIO's 64-bit connection so that I could insert my custom headphone EQ filters if I wished, but I listened with no EQ (flat) to all my tracks. With the Pass driven by the Callia's unbalanced output, I was able to produce a "loud" presentation of a well-recorded popular music piece at -11dB digital attenuation. Acourate Convolver dithers all its outputs, so there's nothing to fear from its digital attenuation. This leaves up to 11dB available gain, enough to play the softest, widest range classical music piece in my collection. By contrast, the Mjolnir had additional available analog gain, conceivably to play even softer music, but I have never seen any recording that would require it, so I am convinced that the Pass has adequate voltage gain to handle any music you might decide to feed it.

Lindsey Webster "Back To Your Heart"

This is one of my own masters, at 2496. It's a full-bodied, full range smooth jazz recording. With the Pass, the sound is very attractive, punchy and fat. The sound is subtly on the warm side: Lindsey's voice sounds warm and intimate. The cymbals are round, clear, yet extended. The ambience seems reasonably wide; I don't notice any loss of separation. Bass is solid and deep.

Switching to the Mjolnir, the sound is also clean, pure, and extended from bottom to top. The recording's ambience stretches pleasantly, it seems a bit more outside the cans than it was with the Pass. Vocal is perfectly centered within my head. All the clarity is there and it's driving the transients effortlessly. I'm quite surprised that the Mjolnir seems a tiny bit brighter than the Pass on this material since I expected it to sound warmer based on previous experience. Bass is big and beautiful. The snare pops. Cymbals are pure and tight. I don't feel we're missing any high end, even though I'm not using the headphone EQ that I'm accustomed to using with the LCD-4s and the Mjolnir.

Switching back to the Pass, I notice the sound level seems to have dropped just a hair. Aha, that's a clue to the sonic difference: I wager that the Pass sounds a hair softer (even though the levels were matched) because it is much cleaner, has far less harmonic distortion than the Mjolnir. This gives the Mjolnir an unfair loudness advantage. I don't think it will ever be fair to compare these two amps at matched 1kHz levels so it's perfectly possible that the sonic differences amount to the harmonic distortion contributing to a perceived loudness difference.

Either way, the sound of the Pass is extremely satisfying, warm, natural and beautiful, just not as bright circa 8-10kHz as the Mjolnir with this particular recording, but we're talking about the tiniest hair, so small that even an expert could not decide which presentation is more "right". There is no "right" when two amplifiers are both this good. And frankly, I could not pass a blind test to determine which amp is playing, as there is more similarity than difference when the two amps are matched at 1kHz.

San Francisco Symphony, West Side Story

For this gorgeous 24/96 recording from Blue Coast Records, I had to raise the digital gain by 6dBattenuation is now at -5dB. On this recording, which I know to be bright-sounding on its peaks, the Mjolnir is a bit more forgiving as it saturates at higher levels and gets warmer via the additional 2nd and 3rd harmonic, while the Pass remains linear. So when the Jets chorus sings loudly, the vocals sound sweeter and more palatable on the Mjolnir than the Pass. But for the vast majority of this recording, except for the fortissimo passages, the Pass sounds beautiful, warm and pure.

It's critical to note that when I play this recording on my speakers, I EQ the high end down or it would sound bright and a bit harsh. So when playing it flat through the Pass I hear the same issues as on my speakers and amp. It's clear that the Pass amp is subtly on the warm side of accurate, and the Mjolnir on the euphonic side, at least on the loud passages. A bit of program EQ would fix the presentation of this recording on the Pass. Recordings differ and some of them need EQ. Live with that!

Janice Ian, Walking on Sacred Ground

This is from the album "Breaking Silence", transferred from the 16/44 CD. I began with my headphones on the Pass amp. This excellent recording, mastered by Doug Sax, brings goose bumps! Doug's great tube transfer chain really makes this recording sound beautiful, sweet and perfectly reproduced on the Pass. The highs and transients in this recording are still punchy and clear without getting fatiguing. This segues into Janis' "Ride Me Like a Wave", which also does not disappoint. This is a very pleasant listening experience. I do not switch the Mjolnir to compare.

"Do You Remember" by Jill Scott.
16/44 from the album "All or Nothing". This Neo Soul album's bass, in tandem with bass drum, goes down very deep. Her voice sounds warm and full on the Pass. The transients really move, and there's effortless power to spare. This a reference recording for the soul fanatic where the touch of hip-hop feel provides the "neo". I do not switch to the Mjolnir.

"Erienda", by Kenny Rankin
From the album "Because of You", direct from the 16/44 CD that I was the recording engineer for. I recorded this song with minimalist miking, primarily a Blumlein pair, in RCA's Studio A, New York City for Chesky Records with a tube chain and custom A to D Converter. Kenny's voice is just as I remember it, filling the hall so nicely. Highly recommended, if I may say so myself. The tone of all the instruments is just right on the Pass. It's pure pleasure. The ambience of Studio A is reproduced and extended well outside the phones. I do not switch to the Mjolnir.

"Speechless", by Laurie Anderson
This is from the CD "Bright Red". Recorded by the great Kevin Killen, mastered by Bob Ludwig, this a mesmerizing and perfect reference for audiophile fans of rock and performance art. Pick it up right away if you are a Laurie Anderson fan. Pick it up even if you don't know who Laurie Anderson is. The drums are among the best rock drums on any recording ever made, ever! The dynamics are impressive and the Pass does it perfect justice, extending the ambience well beyond the sides of my head. Bass drum goes down to the center of the earth, or at least my head. Mesmerizing. Did I already tell you that? I do not switch to the Mjolnir.

FB Pocket Orchestra, "I Lost My Girl from Memphis"
This swing combo is from my 2496 master of the album "Guerilla Jazz". The Pass reproduces the instrumental and percussion transients particularly well, making me rock involuntarily with the rhythm.

My impression is that the Pass is an impressive, impacting and musical headphone amplifier with absolutely no defects. It's musical, slightly on the warm side, yet extremely true to the source.

Matt and David Take a Listen
Let's check the perspective of a couple of young audio ears: my two assistants, Matt Davis and David Corson, with different tastes in music, so let's see how their favorites play on this amp. (I did suggest some of the tracks). Initially they listened without any headphone EQ. Again, amplifier levels matched within 0.1dB at 1kHz into a 110 Ohm load.

Vienna Philharmonic, Mahler Third, 2488 from HD TracksMatt - On this piece I can't hear any appreciable difference between the Mjolnir and the Pass.

David - The Pass is very similar in tone to the Mjolnir. Though it's really close, the Mjolnir has more impact and microdynamics than the Pass. But the tonality is too close to call.

Lindsey Webster, "Next to Me", 2496 MasterMatt - Pass: Dynamic presentation far surpasses the Mjolnir's. In the Mjolnir, the kick drum is more restrained. The vocal doesn't jump forward as much on her peaks. I'm not hearing the 3D quality: This may be because the Mjolnir's slightly warmer than the Pass as a lot of ambience is contained in the high end.

David - The Mjolnir seems to have a boost in the lows below about 100 and perhaps a bit more presence and microdynamics throughout the whole range.

FB Pocket Orchestra "I Lost My Girl from Memphis", 2496 MasterMatt - The Mjolnir has a harshness and a veiled quality compared to the Pass. The Pass is not brighter. The 6k sizzle in the tambourine favors the Pass over the Mjolnir. The Pass seems sweeter in the highs.

David - The Pass seemed warmer on this one, but did not have as much bottom. Makes me think the Mjolnir has a bit of a smile curve. [BK note: I think the apparent multi-personality of the Mjolnir is because of the sonic unpredictability of 2nd and 3rd harmonic distortion. Sometimes it can sound warmer, sometimes a bit brighter, sometimes more dynamic, sometimes less, depending on the content and the listener's orientation.]

Deepest Crystal Black, "And Where Now", hard rock, by IceCocoon, 2496 MasterMatt - The Mjolnir: This is a thick, closed in mix. The sound is flabby. In contrast, the Pass is leaner, translates better. The Mjolnir is muddy, the Pass is clearer. They both express the deep sub range approximately well, but the sonic differences in the low mids can prejudice the impression of the deep bass.

David - The Mjolnir seems to bring out the bass more as well as the vocals seem clearer, more presence.

Miles Davis "So What" from Kind of Blue, DSD upsampled in JRiver to 176.4Matt - The distinctions are very subtle in this particular track. The two amps are very close. These two amps are more matched than not.

David - Seems similar to my previous reactions.

Ray Charles: "Here We Go Again", 2496 from "Genius Loves Company" Anniversary EditionMatt Pass: Does not feel brighter. All signs would point to that since it has a clearer sonic signature. But it feels natural, kind of makes the Mjolnir feel like a murky amp. The Pass has more dimension.

David - Similar to my previous reactions.

Fahrenheit by Telefon Tel Aviv on Tidal – electronic music, aka "IDM" (intelligent dance music)Matt - Even on something this extreme the Pass has a depth of field that I miss in the Mjolnir. But if I heard the Mjolnir on its own it would stand out well. This is not a glaring issue, a matter of (my) taste.

David - It feels like the Pass is a bit warmer here. But the bass is apparently emphasized in the Mjolnir.

Bruno Mars, 2496 MQA on Tidal "That's What I Like" from "24k Magic"Matt - This is a nice, well-balanced master by Tom Coyne, a warm but incredibly punchy track, a great reference. My idea of a perfect EQ balance. There is an additional warmth in the Mjolnir that I don't hear in my studio. The Pass is a more present amplifier, and I hear the sound as I do on my system. This comes down to a matter of taste, which sound you prefer and why.

[Bob: Now I throw a monkey wrench in the works, my LCD-4 EQ] With the EQ, now this song feels thin with the Pass and the Mjolnir sounds more like the Pass did without EQ! It could be that the Pass is imparting a subjective Air band boost. The Mjolnir is more "tubey". The triode-like saturation in the Mjolnir can be desirable.

I really like the cleanliness of the Pass. The EQ helps the Mjolnir but I still can't shake the feeling that there's an alteration going on in the midrange. I can see some people seeking that character but in this range I seek neutrality. Most people would prefer the Mjolnir when Bob's headphone EQ is applied.

David - Similar reactions, except now the Pass seems warmer from 60 through 500. But the really thumpy bass is greater on the Mjolnir.

Summary
Matt enthusiastically preferred the Pass to the Mjolnir. Matt and David sometimes differed in their reactions, a matter of taste, but keep in mind the Mjolnir was designed to emulate a classic triode circuit, which saturates a bit as things get loud. Single tone tests on the Mjolnir show predominance of 2nd and 3rd harmonic. However, harmonic distortion is a funny beast, sometimes it can manifest itself as presence, sometimes as warmth, and often as fat bass, very dependent on the material, so I'm not surprised at the sometimes apparently contradictory reactions depending on the musical source. Distortion is compression, it can subjectively soften dynamics, but when it's enhancing a range, that range can seem louder and counter intuitively dynamics can appear to increase.

There is enough evidence here that the Pass is the more robust amp and technically the more dynamic of the two amps. We also present some interesting evidence that if you adjust EQ for a headphone, be sure to pick the amplifier you are going to use with this EQ. In fact, when EQ was applied, suddenly one amplifier seemed to take on some of the personality of the other. Harmonic distortion can sound a lot like EQ.

In summary, if you like your sound tight, impacting, clear, accurate and transparent with a nice taste of warmth, I would highly recommend the Pass HPA-1. If you like an amplifier that's a bit more forgiving, especially with harsh sources, I would lean towards recommending the Mjolnir. I would not kick either amplifier out of bed!

You can have four of the Schiits for the price of a Pass, or keep one Schiit and give three Schiits away as gifts, or have one Schiit for every bed in your house, if you really want to have them in your beds. I would Pass on that, and kick either of them out of my bed.

It makes me wonder how either sound next to the Cavalli CTH (sweet tube hybrid with lots of juice)..($250..Massdrop), or the Schiit Jotunheim, which is wonderful in "push-pull" mode..and a monster in power...($399 US Dollars)

You can have fourteen Cavalli amps, or... eight Jotunheims,along with one Cavalli CTH, and change....for the price of one Pass Labs HPA-1.

I wonder too, which would work best with an Aeon Flow Closed, at 13 ohms and 92dB/mW effeciency? ...( yes 13 ohms, just 13 lonely ohms.)

Thanks Bob, for all the info, and allowing me to pick your, (or anyones)..brain here.

I would like to reiterate that this amp was not compared to the Schiit Mjolnir 2. I think it's important to pin this down because the comment was made that the HPA-1 is multiple times the price of the Schiit Mjolnir... and that was immediately requested to be compared against amps a fraction of the price of the Schiit Mjolnir. This race to the bottom never stops.

Price is a very important specification to some of us, and the absence of the prices of the two amps here is for me a serious deficiency in the review. While I was well aware that the Mjolnir included here was not the Schiit product, I had no idea what the price of either it or the Pass amp. Including the price obviously would have helped avoid confusion to one reader. I had assumed that the Pass and Mjolnir i question probably were about the same price. The reader should not have to go off on a search to find the prices of the equipment in question.

Based on this review and what other readers have stated as the price, I come away with the thought that the Mjolnir noted is a bargain relative to the Pass--one can buy a lot of music for the $1400 difference! ‘Race to the bottom’ has nothing to do with it.

Price is a very important specification to some of us, and the absence of the prices of the two amps here is for me a serious deficiency in the review. While I was well aware that the Mjolnir included here was not the Schiit product, I had no idea the price of either it or the Pass amp. Including the price obviously would have helped avoid confusion to one reader. I had assumed that the Pass and Mjolnir i question probably were about the same price. The reader should not have to go off on a search to find the prices of the equipment in question.

Based on this review and what other readers have stated as the price, I come away with the thought that the Mjolnir noted is a bargain relative to the Pass--one can buy a lot of music for the $1400 difference! ‘Race to the bottom’ has nothing to do with it.

When the above commentor thought that this article involved a direct comparison between a ~$2500 amp and an $850 amp, it was immediately turned into a request for a comparison to a $400 amp. Same breath. And I guarantee you if the request was granted and the feedback was positive, someone would roll in requesting a comparison with a $200 amp. Then a $100 amp.

Headphone folks do this all the time - when the Xiaomi Piston 2 came out, everyone said it was a $25 IEM that sounded like a $100 IEM. So every time a new $200 IEM came out, threads would be flooded with comparison requests to the $25 IEM - since it sounds like a $100 IEM, etc.

That is the race to the bottom, and if you don't stamp it out immediately, it happens.

I think it is important to include prices for items reviewed, along with meaningful comparisons to other units either costing more, or costing less. This comparison gives us assurance that the product's price actually reflects its performance. For the price of the Pass Labs HPA-1, I could buy a very nice used car. I just saw a 2006 Chevy Impala, police package 137K miles, for $3,500.,or a 2002 Audio S4 Quatro...same price.

What 'extra' spending money I have, I wold much prefer to spend on music, than on audiophile hardware that doesn't really fit into any rational scheme of value. I would really love it if reviewers would give themselves and the rest of us a reality check, and cover up the amps being compared so as to eliminate brand bias, and then make listening notes on various cans, not just one model. To really be fair and useful, these tests must include amps across the board in price.

“I would really love it if reviewers would give themselves and the rest of us a reality check, and cover up the amps being compared so as to eliminate brand bias, and then make listening notes on various cans, not just one model. To really be fair and useful, these tests must include amps across the board in price.”

inner fidelity will probably never do this. And I think you know why they will probably never do this. And will inner fidelity do ABX tests of headphone amplifiers volume matched to within 0.1 dB? Outrageous! What do you think this is? hydrogenAudio?

What I ask for is reasonable. If these listening tests are to have any semblance of objectivity, and most importantly, to be of any use at all to readers.
This review tells me nothing meaningful, actually. Who could be persuaded to hunt up this illusive amp with so little actual information about it that matters, not even considering the enormous price tag, which was never mentioned in the review? Seems a fools game to me.

I am almost in complete agreement with you. This “review” was written, it appears to me, for two groups of individuals—those that might spend 3500 to 130 000 USD on a headphone amplifier and those that, while they may not be looking to buy a headphone amplifier in this price range, are, nevertheless, inner fidelity’s most important readers; for this second group of individuals, this review is, I am convinced, very useful.

Sighted reviews are like the p-value of statistical inference.
They seem to convey the information that people want to know but actually give you the opposite.

People want to know the actual performance of the device given the test results, but sighted reviews give you subjective impressions (the "sighted test results") given the device.

This is not only backwards, it is fundamentally flawed.

And we've all seen what this leads to for decades now. People praising devices heavily influenced by price tag, prestige ... and then when someone actually listens using their ears (I know, that's shocking!) or measures we find out that the device is performing abysmally.

If we depended on blind reviews of amps, there would be no sonic difference between Class A, Class AB and Class D, yet critical listeners agree that there are audible differences. I do not perform blind listening comparisons anymore because the subtle differences are simply masked by the noise of the testing procedure. However, that does not mean that sighted reviews are any more reliable or consistent, that is the dilemma. If you do not judge my sighted reviews to be worthwhile or reliable, then why do you read any of them? For your entertainment? Then don't complain. Some people actually respect my opinions, which are more informed, more qualified, and more unbiased than a lot of other subjective reviewers opinions. But I am not perfect, and you must learn to read between the lines. But your knee-jerk reaction recommending blind reviews of amplifiers will simply result in null results for the most part. This goes back to blind reviews showing that amplifiers with 1% THD sound no different than those with 0.001% THD. Why? Because it's extremely difficult and expensive to conduct a valid blind test for subtle differences. And don't try to tell me about your latest casual blind test.... the chances of it revealing a difference when there is one are very slim. The chances of it seeming to produce a null result and concluding "all amplifiers sound the same when at the same level are very high. So who's right? The blind testers? It's the only scientific way to prove. But far more costly and time consuming than you can imagine. I've been there, and done that, conducted some very costly (in time) and successful blind tests, and I cannot imagine doing that for every single review that I publish in Innerfidelity. So quit your knee-jerk reactions, quit your repetitive bellyaching on the same topic. It always will boil down to "subjective tests are bad, blind tests are the only thing, yet these blind tests for the most part reveal nothing but "no sonic difference". Why? Because they are far more difficult to perform than you have any idea, require extreme skill and knowledge to perform right, and can take months to years to reach a valid conclusion.

Enough said. Stop posting about blind tests. For the most part I'm not going to do them for this magazine. If the occasion comes up where it can be done with little cost and time, I may perform one.

You say that "if we depended on blind reviews, there would be no sonic difference" but "critical listeners agree there are audible differences".

Audible difference means a sonic difference that is perceivable through hearing (that's the ears and not the eyes), so what you said above makes no sense.

"subtle differences are simply masked by the noise of the testing procedure"
I've heard plenty of excuses why not to do blind tests, and none of them have stood up to scrutiny.
What you are effectively saying is that you cannot reliably hear differences.

Then when do you hear them and how do you know?
... right. And that's the problem with sighted reviews.

How do you distinguish "critical listeners" asserting that they hear a difference although they don't and a person actually hearing a difference?

What is the difference between a "critical listener" asserting that some devices improves the sound and a person asserting that globules (sugar beads) cure diseases?

"it's extremely difficult and expensive to conduct a valid blind test for subtle differences"
It may be difficult for reviewers that are used to hearing with their eyes (not referring to you specifically) to actually listen with their ears .. to that I agree,
but it is not expensive.
You again make excuses that are demonstrably false.
Just with a few trials you can actually provide positive evidence for the hypothesis that you can hear an audible difference .. and this is the basis for a review on the sound. Not even for the readers but for the reviewer him/herself, so that he/she can answer the above questions at least with some confidence.

Btw, the magnitude of the sonic difference per se is irrelevant. In simple blind tests we usually don't test for the magnitude of differences, but whether there's any audible difference.

Or are you again saying that the sonic differences are so small, that the reviewers could not tell the devices apart without peeking? Then why do a review on the sound?

"quit your knee-jerk reactions, quit your repetitive bellyaching on the same topic"
Why are you so offended? I have neither brought up the topic, nor have I commented more often than maybe 2 other times over a timespan of several years on this site.

I haven't even suggested that you do a rigorous DBT... After you've calmed down, maybe read my reply to zobel again.

In case you skipped all of this in anger,tl;dr
Blind comparisons (i.e. listening with your ears) are an invaluable tool for audio reviewers.
In fact, they are the basis for making sensible comments on sound.

In closing, I have to revise my initial statement about the p-value:
You say that "if we depended on blind reviews, there would be no sonic difference" but "critical listeners agree there are audible differences".

Audible difference means a sonic difference that is perceivable through hearing (that's the ears and not the eyes), so what you said above makes no sense.

"subtle differences are simply masked by the noise of the testing procedure"
I've heard plenty of excuses why not to do blind tests, and none of them have stood up to scrutiny.
What you are effectively saying is that you cannot reliably hear differences.

Then when do you hear them and how do you know?
... right. And that's the problem with sighted reviews.

How do you distinguish "critical listeners" asserting that they hear a difference although they don't and a person actually hearing a difference?

What is the difference between a "critical listener" asserting that some devices improves the sound and a person asserting that globules (sugar beads) cure diseases?

"it's extremely difficult and expensive to conduct a valid blind test for subtle differences"
It may be difficult for reviewers that are used to hearing with their eyes (not referring to you specifically) to actually listen with their ears .. to that I agree,
but it is not expensive.
You again make excuses that are demonstrably false.
Just with a few trials you can actually provide positive evidence for the hypothesis that you can hear an audible difference .. and this is the basis for a review on the sound. Not just for the readers but especially for the reviewer him/herself.

Btw, the magnitude of the sonic difference per se is irrelevant. We don't usually test for the magnitude of the difference, but whether a listener can hear a difference.

Or are you again essentially saying that the sonic differences are so small, that the reviewers could not tell the devices apart without peeking? Then why do a review on the sound?

"quit your knee-jerk reactions, quit your repetitive bellyaching on the same topic"
Why are you so offended? I have neither brought up the topic, nor have I commented more often than maybe 3 times in a couple of years on this site.

I haven't even suggested that you do a rigorous DBT... After you've calmed down, maybe read my reply to zobel again.

In case you skipped all of this in anger,tl;dr
Blind comparisons (i.e. listening with your ears) are an invaluable tool for audio reviewers.
In fact, they are the basis for making sensible comments on sound.

In closing, I can only repeat my initial statement: Sighted reviews on sound are like playing tennis without the net and without the line markings.

I'm with Xnor on this one. If you must know which amp you're listening to in order to tell a reliable difference, it begs the question: can you reliably tell the difference?

Many people who are reading these reviews are expecting to get to truth on these products. If you're not telling them that you'd be hard pressed to notice any difference in a blind test, then I'd argue that you aren't being completely up front with them. I would furthermore encourage people like Xnor to reply and point this out, since you didn't.

And a blind test doesn't have to be as exhaustive as you are insinuating. I would argue that any form of blind test is better than none at all.

"I would argue that any form of blind test is better than none at all."

Here is where we have to agree to disagree. I've been trained on how to conduct blind tests by two of the world's experts, psychoacousticians in fact. These people do not take their responsibilities lightly. I'm sorry to have to break the news to you: There is no such thing as a "casual" blind test.

Expert listeners are listeners who have either trained themselves or been trained to hear sonic differences which many others say they cannot hear. Therefore, Blind tests on subtle differences may require months of training, an expert trainer, and many trials in order to reach a statistical conclusion.

That ain't gonna happen here, at Innerfidelity, let me break the news to you. And I'm not going to conduct anything less than a proper blind test, with the proper protocols, which requires far more expertise and training than you can imagine. To touch the surface of it, you can read up a bit about the protocol "BS.1116". Google it. One of the cautions by one of the authors of the protocol (who is one of my mentors on blind testing, by the way) is that this cannot be taught by "reading the manual", even though the protocol has been delineated. It also requires training and mentoring.

So I am humbled as we all should be by this dilemma: A casual blind test on a subtle difference is almost always destined to fail, to seem to show that there is no audible difference. We've seen this again and again. Does this mean that there is no audible difference, or that the listeners have not been properly trained to hear the difference, or that the method of the test was insufficient to allow them to hear the difference.

It's a dilemma that continues to trouble me in particular, as I'm currently in a debate about a subtle technique which hundreds of trained audio professionals work with every day, with the premise that we CAN hear and operate on that subtle difference. But the naysayers claim that such a difference should not be audible. Furthermore, blind tests on this difference have so far come up null. Imagine if you were a working professional who has used a particular technique for decades, each time coming up with a useful result to your ears, and your technique has been questioned by others (perhaps not so expert listeners).

So, please rest.... give the topic some rest. I'm quite sincere in my reviews, I've been at it for many years, but you're not going to get a blind test from me unless you can pay my salary for a year so that I can devote my entire energies to a proper, non-casual blind test on the topic at hand. I'm sorry, it's not going to happen.

Bob, I appreciate and respect your knowledge on all this stuff. I enjoy reading your columns. However, on the subject of blind testing I find myself disagreeing. While I would agree that if you want to have scientifically valid information it is crucial to follow a very specific set of standards that may be difficult to execute. But it seems to me that a sighted test would contain all the same flaws that an imperfect blind test would contain, and more.

What is the harm in following similar procedures that you use in your testing, with the only exception being you don’t know which amp is which? That wouldn’t be difficult to do at all.

Perhaps:

-Set the volume of each amp at as similar a level as you can (to avoid having to adjust during the testing, thereby revealing which one is which)

-Have someone set one as “A” and the other as “B”. Have that same person change what is “A” and what is “B” a few different times.

Something like this seems simple enough. And while it wouldn't necessarily stand up to the scientific method to be considered statistically valid, I still think it could provide more valuable information than a sighted test.

If you did something like this, do you think you could reliably tell the difference between the two? If not, then surely it begs the question: is there any difference? And if there is, is it possible that difference is too small to meaningful?

I know where I stand: if I can’t reliably pick out differences between two things without knowing which is which, than any differences that exist are too small to be meaningful in any way.

Now that I have your attention, a separate topic: I have been wondering if you are ever going to do a review on Sonarworks EQ. I would be interested to hear your opinion on it. I tried it out. I thought it sounded off at first, but now I absolutely love it and would never go back.

Thanks for your kind words. In my lifetime I've performed and participated in a few carefully-prepared and matched blind tests and for subtle differences they usually come out null. I have studied how to perform blind testing and taken lessons from two of the world's experts, who are both very quick to point out that blind testing must be rigorous, require great preparation and trained, experienced testers as well as trained subjects. So I humbly usually refuse to venture into that world, and I will not perform a casual blind test, which is the vast majority of blind tests that you have heard about.

One exception was a test of jitter with 20 to 30 participants that was very enlightening. The amount of preparation required weeks, dedication from myself and a partner and rounding up many participants in order to get a statistically-meaningful number of trials. It's not easy, despite what so many blind test adherents claim.

So it either means that there are no sonic differences between things that I hear sighted, OR that the resolution of the blind test (for whatever reasons, including method, training of the tester, training of the subject, inadequately-chosen musical samples, etc.) is not sufficient.

So 'll wait till there's an issue worth arguing over, because a rigorous blind test of subtle differences requires many trials, can take weeks to months, require proper training of the subject(s).... Even then I've seen these fail more often than not. You bring up the question that if the difference is so tiny, why is it worth arguing over, and I respond that I believe the resolution of a blind test is often an order of magnitude worse than actual human perception. Now that's not a claim that I can prove, but it is also not a claim that advocates of blind testing can disprove! It's just a hypothesis that I have.

So those who advocate strict blind testing make their arguments and those who advocate or perform sighted testing make their arguments. Of course I subscribe to scientific method most of the time, but I am also an artist. In my column I choose to express my sighted opinions. Hopefully they seem sensible and reasonable to you, but if not, hopefully they are entertaining :-).

I've been resisting Sonarworks for some unknown reason, eventually will look at it for this column. I have my own research on headphone correction that's getting closer and closer to reality and wish to perform that first.

Blue Book pricing on both cars you mentioned starts in the $5000 range. If you find them for quite a bit less than that..... they probably have major issues.

Not to mention the comparison is absurd from the start. For $3500 I can buy a really nice dog. That companionship they will bring is worth far more than any headphone amplifier. It could also feed a homeless family for at least several months. Again, all pointless comparisons, just like yours.

If I might ask an important question. Why do you bother posting here? You seem to actively dislike every review you've ever commented on, so why not do yourself a favor and find another site? I'll never understand this mentality. I don't go hang out on NASCAR forums or sportfishing forums complaining about how I dislike those "sports". It kinda feels like that's what you consistently do here.

What a review! It is the responsibility of a reviewer to find the value of equipment being reviewed. Tyll does an excellent job of this, and avoids reviews weighted towards price tags, meanwhile making fair comparisons between cans, regardless of cost.

The thing I respect most of any reviewer is an ear to value. What does the product provide for your money? Tyll constantly keeps the highest performing headphones on top of his wall of fame list, but will kick off the poorer values in head to head comparisons, all else being equal.

Many of the products Stereophile recommends are not even close to good enough for the money, and are often out performed for less money. I think this is no doubt true in this headphone amp recommendation. Therefore, it is just a tire kick.

Just like my comment to XNOR above, why do you hang out here when you seem to loathe so much of what is written on the site?

Also, you are basically saying "some other magazine often recommends gear which I feel is not the best value. I bet the same thing applies here." What a useful comment! Thank you for sharing your expert opinion, random internet guy!

If you have an opinion, why not express it? I already expressed mine, and shared what I like and don't like. Perhaps you could read what I've posted with an open mind, or at least read it at all, before commenting so snarkily.

My issue is why people like you and XNOR bother visiting this site, since you very obviously have long-standing complaints about the nature of the reviews. It's like going to a NASCAR forum and being mad that they never make right turns.

So after this, are you going to head over to a hunting equipment review site and convince them meat is murder? Then a food critic blog and comment how you'd respect her opinion more if she was vegan? Then it's on to a homeopathic remedy blog to demand evidence-based treatments? You see the folly in these things, right?

Seriously, whether you agree with any of those stances or not, you have to understand that you are basically doing the same thing here. Asking Tyll (and the other contributors) to make this site into something it clearly is not, seems like a pointless thing to keep chasing. Tyll created the site the way he wanted and has had many years to rethink that if he really wanted to. It seems he does not, but you persist. Can't you find another site more suited to your sensibilities? Or at least have the self-control to stop demanding change to the vision they have here?

"are you going to head over to a hunting equipment review site and convince them meat is murder?"
No, but if I was into hunting and they used water guns, I'd give them advice on more effective weapons...

"Then it's on to a homeopathic remedy blog to demand evidence-based treatments?"
So you are comparing innerfidelity with a homeopathic blog? Wow.

"You see the folly in these things, right?"
The patent absurdity of your straw men? Yes, I do.

"you have to understand that you are basically doing the same thing here"
Nope, still wrong, as is the rest of your post..

So let me ask the question again, that you have evaded:
How can you not make suggestions on how to make audio reviews much more credible and useful? It's like you want to be fooled or maybe even want to fool others.

Either you aren't hearing me, or you are deliberately pretending to miss my point. Maybe a combination of both.

The issue here is this: you have a perspective which you feel is better than the one put forth by Tyll and InnerFidelity. You would clearly like to see the general approach around here change. Hence your "suggestions" on how to make the reviews here "more credible". After many years, it doesn't seem Tyll and Co are interested in making that change.

At what point do you stop pestering them (and us) with your "suggestions" on turning this site into something it is not? My comparison with homeopathy was valid, not because I think this site is also woo-woo, but because that's also not the sort of thing where you can change someone's mind with a quick comment. Like politics or religion or a host of other topics, nobody likes "that guy" who shows up in the comments and tries to educate everyone on why they are wrong. Has that ever done anyone any good? I think not.

It would be like me going to Analog Planet to let them know how inferior vinyl is... might be a strong opinion of mine, might even be objectively true, but what would be the point? All that would do is cause strife. Better to head over to a digital-oriented site and participate there in a more meaningful way.

The take away is this. You should either stick to hydrogen audio or some other site that fits your sensibilities, or else humble yourself to accept the "flawed" approach they take here, and enjoy it for what it is.

"stop pestering them (and us)"
You gotta be insane making such a comment. You still don't get the point.
You again evaded my question. 2x now.

And the only pestering I see is coming from you, dishonestly and blatantly alleging defamatory and patently absurd things.

"My comparison with homeopathy was valid, not because I think this site is also woo-woo, but because that's also not the sort of thing where you can change someone's mind with a quick comment."
If all I'm hitting is closed-mindedness then no.
But is this your general attitude? Don't even try to improve anything? That sucks.

"what would be the point?"
If you don't care about what is true and prefer to fool yourself or other people then absolutely nothing.

"humble yourself to accept the "flawed" approach they take here"
I don't think you understand what comments are for.
They are not just for yea-sayers and sycophants.

I also don't think that you know that I've talked with Tyll e.g. about the headphones measurements/procedure when this site was still in a planning stage.

I also wanted to do the live headphone graph visualization/comparison - I had already started (this was years ago) - but it somehow fizzled out.

And this seems to be another strawman of yours, that I don't enjoy what is produced and presented here.
Please go troll someone else.

You are telling us that you already made your thoughts very clear to Tyll since the very beginning of this site? That makes it even *worse* that you pop up so often, making the same sort of comments. Ok, we get it, you want a certain type of process for reviews, and find anything else of little/no value. Time to move on.

At the very least, how about more moderate comments such as "You already know my stance on blind testing etc, but I do have a question/comment/etc about the topology of this amp". Or "Did you try sensitive IEMs with it?" "Can it drive tough loads like HE-6 and Susvara with adequate volume?" Or how about "I heard it in my system and loved it/hated it, here's why..."

Those are the types of discourse that add to the site. Your current approach detracts.

No, you are again wrong and quite dishonestly so. You still don't understand and you never will .. because you apparently don't know that to increase your understanding, a normal human being usually asks questions instead of strawmanning/condemning/dismissing based on prejudices.

You also evaded my initial question again.

"Those are the types of discourse that add to the site."
How utterly hypocritical of you, when all your replies so far have been whining, strawmanning, nonsense ...

You're dishonest, closed-minded troll. I don't want anything to do with you unless you seriously change your attitude.
Bye~

I'm sorry I did not mention price in my review. For the record, the Pass HPA-1 retails for $3500 and the Mjolnir Pure Bipolar for $2100. I did not stress price/performance ratios in my review, it was just not my orientation for the review. I was strictly looking at sound. And besides, it's 100% true what I said in conclusion, I would not kick either the Pass or the Mjolnir Audio amps out of bed. If it came down to a spare $1000 I would pick the Mjolnir Audio Pure Bipolar and I do tend to prefer a sweeter, warmer amp for my headphone listening, which is more for long term pleasure and a more forgiving amp makes that a bit more fun.

If, however, I were using headphones for my audio business of mastering, which I do not, I would pick the Pass. Because I need something which is truer to the source for my mastering studio. But I do not use my headphones for mastering, I use loudspeakers. If my amplifier were masking some details in a recording, and my job is to judge that recording, the Pass would be a better choice for me.

I liked Tyll's approach to the amp shoot-out. Short of an ABX test, at least it was a blind test in which no one knew what they were hooked up to. Also, the use of different headphones on the amps was ear-opening.

I realize that you, Bob, are no stranger to a more disciplined approach to equipment evaluation (with value as part of that evaluation), but this comparison points out little that couldn't be said when comparing any two amps, at all price levels. There is no scale at all in that yardstick. I think you actually hit the nail on the head, though, by asking why we read your review. That is almost as important as asking why you wrote it in the first place. It is just your casual impressions about two expensive amps, xnor-ing any objectivity, or relativity to other amps, or compatibility with various headphones, not to mention price/performance considerations.

Also, it isn't upon you to tell people what to post about. Xnor has every right to call for blind testing. He is 100% correct in his assessment of the validity of sighted testing. Take your own advice. If you don't like what he is saying, don't read or comment on it. After all, this is a forum, for which you were paid to contribute an article. It is best that others are able to disagree with you. I contend that little is learned by reading totally subjective reviews that do not include a good sample of items being reviewed, and in the case of amps, an assessment of performance with a wide range of headphone types. The impression that one of these amps you tested sounded more analytical than the other, and therefore, your intended preferred use of either amp, would be completely altered by which headphones you are using. For example,if you listened through a Semmheiser HD 800s to these amps, you probably would have kicked that Pass amp out of bed, and made love to the Mjolnir Pure Bipolar.

Life of the party, give an explanation of how audiophiles can hear a difference even when audiophiles cannot hear a difference. And while you are at it, tell us why the earth is flat. Tell us why the sun orbits the earth.

I give you an explanation of how readers can enjoy audio review sites even when the don't completely line up with our philosophies in every single way? Instead of the term SJW, you are an Audio Justice Warrior. Again, that sounds like a lot of fun.

Well, I did not really believe that I was going to change your opinion or the opinions of other audiophiles already set in their ways. I have already stated the reasons why this is very unlikely. But there might be one or more individuals who are wondering if it is possible for inexpensive amplifiers to sound like expensive amplifiers. Is there evidence to support this—perhaps radical—claim? My comments have been directed more to these individuals than to those audiophiles that have beliefs that cannot be swayed.

Since inner fidelity has a comments feature, I have assumed that I am—within reason—allowed to make comments on the articles. Mr. Katz has already stated his belief that all amplifiers sound different from each other. I, however, feel that it is very reasonable to provide a dissenting opinion and a test methodology that supports my dissenting opinion. Can readers that have increased knowledge still enjoy audio-review sites? I think it might be possible.

I have no intention of buying the Pass Labs HPA-1 or the Mjolnir Pure Bipolar in the foreseeable future, just as I have no intention of buying most of the audio gear that is reviewed here. That doesn't preclude me from appreciating a (sighted) review and comparison from someone who obviously knows his sh*t. Thanks for your contribution Bob.

In my review my goal was to express some new ways of looking at the differences between two amplifier designs, which happen to be expensive amplifiers, but that was not the purpose of the review. One important point, for example, is that if you would like to equalize for your headphones, you have to take the amplifier into account. It's clear from the review that the EQ which I designed for use with the LCD-4s and the Mjolnir, would not be appropriate for use with the Pass.

On another topic, I'm sorry that in the comments I went ballistic and made my opinions about the weaknesses of blind testing into a diatribe. I do have my opinions, but it's disrespectful for me to express them in Biblical initiatives :-). We sometimes overreact when our buttons are pressed, and my buttons were pressed this time, I apologize!

I get itchy about prices. Your work is good, and your insights are appreciated. I do give them the value you would expect me to...Its just that I wonder very strongly about the value of the equipment at the prices they're at. It is just money...https://www.youtube.com/watch?v=hJ9yBgTp9UQ

I my opinion reviewing expensive conventional headphone amps in 2018 is a bit like reviewing a typewriter in the 1990s. The best amp is no amp at all, and that is what Rob Watts as arguably one of the best (many would say the best) DAC designers in the world has taught us.
For "only" 2700$ you can buy the Hugo 2, a DAC/Amp, which I am very sure is better than the Amps considered in this review PLUS whichever Dac Bob might have used (some conventional chip based Prism Dac I guess). Probably I may be wrong, because I am not an engineer with technical expert knowledge, but I definitely think it's not possible to ignore the Dac/Amps by Rob Watts, because their singular concept offers much more for much less money than conventional reference products.
Here is a link to a very informative lecture by Rob Watts:https://www.youtube.com/watch?v=BXyjsSYjnL8

The new Mytek Brooklyn has a good reputation for its headphone amp as well. Depending on your outboard gear and processes and how you use them, it may not be convenient or useful for you to incorporate your headphone amp within the DAC. I have over 6 headphone amps connected to my system (I know, that's unusual, but I'm a reviewer) and two DACs. And an outboard analog processor/preamp, so the only way that could be patched is between the DAC and the headphone amp. If a DAC has an integrated headphone amplifier, I would now recommend that the manufacturer include an insert point for use with external processors/equalizers. The reason for this recommendation will become quite clear after the next installment of Katz's Corner, upcoming Episode 25.

Bob, with the products by Rob Watts it's something different. It's not a Dac + Amp in one housing, it's rather more like the Dac in itself is the Amp. There is no other product on the market - at least to my understanding - which works that way. Therefore there cannot be an insert point for external processors.

I wonder, have you actually heard any of the devices you are talking about? Even the Hugo 2? Or is your whole thing based on the cult of personality Rob Watts has built up via HeadFi marketing?

I'll tell you my thoughts on this. I have owned many Chord products over the years, and currently have a Hugo 2 and DAVE. I enjoy them for what they are. But I also understand why some people really dislike the sound. They just don't work in certain systems. Also they are much better DACs than amps. Driving my HD800S out of the Chord gear directly is not my idea of a good time. Yes, that includes DAVE. Some call it clear or transparent, I call it a scalpel cutting directly into my brain. No thank you.

Watts is clearly a smart dude. So are the other designers doing FPGA magic like Ted Smith at PS Audio, Dustin Foreman at Resonessence, Jim Kinne at Exogal, Ed Meitner of EMM Labs, Andreas Koch at Playback Designs, just off the top of my head. These guys are all very clever and have many achievements under their collective belt.

The difference in my view is that Watts hangs out on HeadFi and directly markets to the community. The result is people like the above poster blindly parroting things they have read, without any real context. Do this long enough and it becomes gospel. The weird thing is, if there's anyone out there worth blindly following due to reputation and achievements, wouldn't it be Nelson Pass?

Ok, find the weak link in your argument: it's the same weak link of your impressive chain and named HD800S. No wonder, you need some added harmonic distortion to make it sound more pleasant... . Seriously: it's not the Dac's fault that these sound harsh. With your budget I'd rather sell DAVE, stick with Hugo2 and buy better headphones. Frequency-wise HD800S is flawed. Seems like somebody has fallen to marketing, eh?! ;)
It's funny that somebody like you who's choice of headphones is at least questionable, tell's me how much more capable his hearing is in assessing amps and dac's...

That was just one example, I could swap it out for my Utopia or Ether Flow or SDR HD800 and the point would be the same. DAVE does better with my Audeze, ZMF, and Hifiman planars but when compared to a quality amp (like the Pass) the Chord shortcomings become pretty clear imho. It doesn't have the best timbre and can't flesh out some instruments to sound like they do in real life. Again, the DAC is better than the headphone out.

Some folks love DAVE as an all in one DAC and amp. That's a fair point but let's not pretend it's anything beyond a currently popular choice, with a large part of that popularity being owed to Rob using HeadFi as a marketing platform. There are many, many people out there who prefer Schiit's Yggy to the Chord stuff, to name just one example. If you love R2R DACs you probably won't be satisfied by even the best Chord product. So let's cut down on the groupthink here.

let’s unpack your post starting with the typewriter analogy. If the headphone forums are anything to go by, and I think that they are, then it looks unlikely that expensive headphone amplifiers will suffer the same fate as the typewriter anytime soon. Rob Watts is undoubtedly a talented DAC designer but his is one approach. There are others that are arguably just as valid and well executed. There are also DAC/amplifier combo alternatives to the Hugo 2 that can be had for considerably less money. Chord products are not known for their price/performance ratio - consumers pay a premium price for them. And while Chord products have received high praise from reviewers and owners alike, they’re not for everyone.

You claim that the Hugo 2 is better than the two amps compared in the review and the Prism Callia DAC but what is the basis of your claim? Do you have first hand experience with any of these components and have you compared them to the Hugo 2? I suspect not. You then go on to undermine your own opinion by saying that you’re probably wrong. I expect to see this kind of blind fanboyism over at Head-Fi and that’s where you should have posted - not here.

...that synergy between components is actually more important in our discussion, than which dac, amp, headphone, source, is 'best' ?

That seems to me to be a large part of the fun in audio...finding good combinations of components. I think that always has been the case, and will always be the case. I also enjoy finding the best sound for the money.

To rabid Rob Watts fanboys, there is nothing better in the entire universe. Period. Anyone who thinks there might be is simply listening wrong. They should probably watch more Rob Watts videos or something.

I say this lovingly as a Chord DAVE owner who enjoys it well enough, but can admit that other devices have their own merit.

I tried to carry the Threshold Line in 1985 but they already had someone...

Since the Spring of 2015 when the Pass designer was presenting this Amp's Prototype at RMAF, people have been praising !

It seems a "given" that any Pass Design will be "Solid" A+ Recommended Componant. Isn't it?

So, I suppose that you agree with everyone else.

I checked eBay for "used" Pass gear. hmm, pretty thin offerings considering N.Pass has been making great stuff 4-EVA !

Why review this Amp?

Why no story about it being a Pre-Amp?

or....

that it doesn't have balanced Outputs. Hmm again.

I see a much bigger Picture of this Amp. I see the vast majority of A+ Rated Electronics achieving superior performance levels without the negative drag from having to do Phono levels of step-up and amplification. Phew!

A level ( 2 Volt ) playing field and an Abundance of Repeatable Signal Sourcing from RedBook and higher.

My take is that today's Electronic Designer works to a budget and hits performance levels with consistency.

Beautiful Chassis Packaging is the big additional Cost, strip the pricy boxes and we have Schiity Gear.

So, maybe an Audiophile level review of the New Schiit LYR 3 is in order.

We all seem to entirely agree on every aspect of audio involving reproducing music at home on our stereo systems. No one here has ever felt that they have spent too much for any audio component, or that they might have been duped into purchase of expensive snake oil.

Anything anyone writes here is truth, and should be respected, no, treasured, ...as scripture, and to be taken as irrefutable, and not to be challenged, beyond discussion, as sacred gems of knowledge.

Suggestions of what might, or might not be included, will be taken as heresy. Opinions to the contrary to anything stated by the audio gods will be considered blasphemy. This is why we all kneel, worship, and praise, the experts who have lowered themselves to inform us of the true nature of reality. That is also why we are always in complete agreement on any viewpoint expressed herein on any topic in audio. Soon we will all agree on what is the best music.

Bob listened to the device at length, wrote up his findings, and presented them for the benefit (hopefully) of the readership. Obviously his methods and conclusions won't be universal, and that's okay. That's pretty much how this works.... you read it, take it as a point of information among others, and move on. It's up to each reader to decide if they trust the writer, agree with his methods, like the same kind of music, and so on.

Does anyone really benefit from these wacky comments demanding ABX testing, complaining about pricing, shilling Rob Watts, or calling out Stereophile (for whatever reason...) as a flawed endeavor? "Hey Bob, this review was garbage because you didn't listen to a single bit of 18th century Flemish harpsichord music." "Hey Bob, I feel this thing is overpriced, because another magazine sometimes recommends overpriced gear." "Hey Bob, all amps and DACs sound the same, you are fooling yourself". It's the equivalent of that car you see rolling down the street with a bunch of militant bumper stickers on it... why does anyone think we want to know their unique political views in that context?

You make assumptions. About subjectivity... if everyone was on your bandwagon, vic, and did as you wished, there would be no progress in audio reporting. This is a discussion, and if you have nothing to add to it, why post here at all?

Of course different amps and dacs sound different. That is not something anyone with decent hearing can deny. They don't sound nearly as different headphones do though. That is why it is much harder to find objective parameters to categorize and describe the sound differences, that become increasingly small, when amps and dacs are of decent design.

Tyll has always maintained a link to objectivity, tying his perceptions whenever possible to his measurements. He made an effort to measure amps, and apply those tests to what was heard from those amps, however, he made no real progress there. There is a reason for that. Trying to nail those very small differences down requires a very disciplined approach in testing, as any competent designer knows.

The efforts Tyll makes to relate his subjective findings not only to the cans on hand, but in respect to the competing headphones is greatly appreciated. I always want at least this in reviews. Have you read about his listening regime, that he keeps as a constant, in order to take subjective and emotional aspects out of the picture as much as possible? That is all I ask of any reviewer, to make a fair attempt at objectivity, and relevance, not just in comparison with other products, but also addressing compatibility with other components in the listening chain.

I have never suggested an ABX test to be part of any review, and realize the limitations of that test. ABX test... I think it is very useful and qualifies as a good yardstick, however, not usually a necessary one. I think Bob writes very well, is extremely knowledgeable, and have enjoyed many of his articles. I have learned a lot from him. This particular article is not anything of use to me, and I think it has very limited value to anyone, outside of entertainment. You are entitled to your little opinion as well vic. Stop trying to 'correct' me. Your lame analogies are a slap in the face, and I find your attitude in offering them to be very rude. Please stick to the subject being discussed. I'm not the subject. I could go on a rant here about you, but that too, would be a waste of time.

In my view, Tyll and the other contributors are pretty well established. You know what they have to offer and what they don't. It should not be a surprise by now. None of them seem interested in replacing the late Peter Aczel with his Audio Critic approach, yet you and XNOR won't be happy with anything less.

I find it incredibly rude of you to keep commenting on how little this article has to offer. Obviously Bob did a lot of work and is presenting his conclusion in a way that he feels is meaningful. If you don't care for it, that's totally fine, but why do the rest of us need to be reminded of that after each article you aren't thrilled with? Nobody comes here wondering if a particular review has earned the Zobel seal of approval.

I strongly dislike Jonathan Valin over at TAS but I don't feel compelled to go post on each of his reviews to tell him he is worthless. Instead, I just steer clear of his work. Problem solved. Saves me a lot of hassle, and saves other readers from having to see my grouchy opinion. It's win-win. And I don't at all feel I'm somehow missing an important opportunity to "improve audio journalism" as that's simply not my job.

@Bob Katz. did your opinion on agreeable distortions and less negative feedback lead you to Pass gears or did Pass push you toward your actual opinion on NFB and consequences? ^_^

I'll leave you alone about blind testing. I have strong feelings on the matter of what defines a listening test, very similar to xnor's, but there was no rule saying that you couldn't come here and share a subjective experience with us. Tyll does just that all the time and we don't crucify him on every single article.
so I think you deserve the same tolerance and I'll bring my Spanish inquisition toolkit another time when test method is the main topic >:)

Someone who is fair-minded and asks good questions! I'm still formulating my opinion on NFB and in fact my next episode, upcoming Episode 25 deals with the issue of NFB EXTENSIVELY and makes some strong experimental discoveries (sighted, though, sighted). Anyway, I've had the opinion that less NFB is often a good thing for a long time. But generalizations are just that, and unless I get into issues of open-loop bandwidth, open loop gain and harmonic distribution of the NFB'ed device, then they are just generalizations. That's why I wrote Episode 25, which I hope you will find to be a groundbreaking investigation and conclusion about these things we've only buzz worded for a number of years. So please stay tuned for the fireworks.

As for blind testing, I'm VERY close friends with two of the world's psychoacoustic experts on blind testing. After much discussion and some rigid, expensive, time-consuming blind tests which I did myself, the bottom line I have to say is: if you cannot blind test correctly, with BS.1116 protocol and proper training on how to use BS.1116 protocol, you're better off sighted. Because your results are likely to be null, and just support the conclusion that there is no sonic difference. Some of the most silly audible things have been shown statistically as likely inaudible. It's it a bit silly to advocate a test method which historically has shown that statistically, almost no subtle difference is audible? So we're in a dilemma: sighted is unreliable, blind is very difficult to do right, so time-consuming to do right.... And I'm ok with that dilemma and I work sighted most of the time.... that's the only practical way as there are so many questions, and so little time. Remember also that I am a professional mastering engineer, I make subjective judgments and preference decisions many times a day, sighted.... rarely do I perform them blind. And people pay me money to do that! What a wonderful thing! And people like my work, too. Another wonderful thing. Is my work consistent? Is it reliable? Is it sometimes flawed? Answer: As much as humanly possible. Imagine doing a blind test on that +0.1 dB at 20 kHz EQ that I used yesterday :-).

I don't have the time to respond in more detail. It's not an argument anyone can win, on either side. The science has the leg up on not being fallible, if the statistics show high enough percent correct. No question. The sighted tester has nothing to go on except his or her credibility, reputation, and integrity, and relative infallibility, or, if you prefer, entertainment value!

So, thanks for postponing the dialogue about blind testing for another moment. Please make sure you've studied BS.1116 before discussing, though.

I don't want to further a pointless argument, but I think it would be an enlightening experience to shift perspective. So audio is a hobby and how we approach the hobby varies greatly. Whether someone wants to put more weight into personal sighted impressions or want to hear about blinded comparison testing is really a consumer choice, no big deal really.

Things may be a bit interesting if the principles being discussed about is moved out of the field of audio and into something else, like the field of medicine. So medicine is considered to be very strictly adherent to scientifically rigorous protocols right? You would imagine everything the doctor recommends to you definitely has some really strong evidence and testing behind it. When a life-altering drug/treatment being is offered to you or a loved one, do you ever stop and wonder how strong is the evidence backing it is? Is it backed by a double-blinded placebo-controlled clinical trial (aka Level I evidence)? Or maybe it is simply the subjective consensus opinion of experts in the field (Level III evidence)? Or maybe its a recommendation without any prior testing or published literature supporting it?

And the scary thing is that the answer can range from any of those choices... even when your life is on the line.

So take a breath and relax, no big deal if some audio impressions are sighted and may be prone to some inaccuracies or bias.

Next time you are in the hospital with a possibly life-threatening condition, the doctors will not be conducting any blinded experiments. They will be making a sighted and biased judgement call based on their personal prior experiences. Maybe there was a prior blinded clinical trial that happens to matches your situation showing good evidence on the treatment options and outcomes. Then again, maybe not. On average it costs around $1.3 billion to run a drug through the FDA's phase I/II/III trials.

Regardless of the specific field or specific protocol, anyone who had the pleasure of going through the tedium of creating an experiment that is double-blinded, minimizes confounding variables, has enough statistical power to produce a worthwhile result, and survives critical peer appraisal prior to publication knows that it is a hell of a lot of time, money, and work for sometimes extremely disappointing results. Reading literature on those studies is also a huge pain in the ass. The majority of studies end up being inconclusive at the end of the day and recommending further studies. Only after enough studies are published on a subject, does actual clinical practice begin to shift, and even then it is usually a very slow shift with behind-the-scenes politics and special interests also hindering things.

Rigorous standardized testing is hard and inconvenient. And doesn't always lead to fruitful results. And many times people just don't bother regardless of the stakes. This is life, not only in audio, but in every other field.

So sometimes when an overly inquisitive patient asks too many questions and isn't cooperating with the treatment plan, you just quote some random medical jargon of semi-related information from latest article of the NEJM and say confidently, trust me I'm a doctor.

"if you cannot blind test correctly, with BS.1116 protocol and proper training on how to use BS.1116 protocol, you're better off sighted."

I'm sorry, but if you had actually understood BS.1116 you wouldn't say something so absurd.
The "careful experimental design and planning" in BS.1116 is so that you don't end up with useless results that approach the uselessness of sighted tests.

So if you don't do a careful comparison, you're screwed anyway .. which is why people hear all kinds of (contradictory) things.
Sighted just makes this situation worse.

Also, you're again using the same bad excuse.
Nobody here is asking for a scientific study, so stop using the excuse that you don't have the time to do one.

How do you not understand that a blind comparison is necessary, especially for yourself, to produce the evidence that what you hear is not biased?

--

In the other post you essentially said that you cannot hear differences reliably.Then when do you hear them and how do you know?

How do you distinguish "critical listeners" asserting that they hear a difference although they don't and a person actually hearing a difference?

What is the difference between a "critical listener" asserting that some devices improves the sound and a person asserting that globules (sugar beads) cure diseases?

PS: The consistency, reputation, honesty .. of the person is irrelevant.
I hope you do understand why that is.

I believe you are mathematically challenged, XNOR. (Surprising, given your pseudo-intellectual "xnor" username).
The "x" is an OPERATOR.
BS times 1116 = bullshit x 1116.
Which is precisely what the ITU is: a worthless, bureaucratic organization along with its hubristic parent, the United effing Nations.

Damn, this is a tough crowd. It's great to get opinions from a knowledgeable professional who is also an audiophile with decades of experience with a variety of equipment and has learned enough to be fair without any axe to grind for or against particular technologies. Sharing opinions from others was even better.

Well designed and built amps driving the kind of loads they were meant to drive will always sound similar even with revealing transducers. That's just a fact of life. But just because differences will be subtle doesn't mean they sound the same. And while a DBT is necessary to *prove* the audibility of sonic differences, the converse is not necessarily true: just because differences do exist doesn't imply a DBT will always detect them. If you believe you heard a difference but can't pick it up in a DBT, they might still exist you just can't be sure. But that doesn't mean you can't share your experience, especially in the transparent way that Bob does.

One request for when you review these super expensive ''TOTL'' components is to have a sensibly priced challenger to see just what you get extra when you pay a lot more (if anything)

For example if you have an RME-ADI2 DAC ($999) on hand when reviewing the Pass HPA1 or Benchmark HPA4 I would be very interested to see if you can hear anywhere close to $2K worth of extra performance.

Amir at Audioscience review has the RME and measured it with excellent results.

The Oppo HA-1 is extremely well designed and built with excellent specs. We can still read the Innerfidelity review from a few years ago when it first came out. But it was never directly compared to these other amps that cost several times its price. Doing so might help answer the question: what is the least expensive headphone amp that can drive just about any headphone and is indistinguishable from SOTA reference quality?

I tried to use my Oppo HA-2 for a review a while back (in fact I reported it) and discovered it will not charge while it's in use! That pretty much limits the use to portable applications. i was always interested in the HA-1.... And it would make a good shootout against headphone amps costing 2 to 3 times as much. Especially nice at the ~$1000 price of the HA-2 is the balanced output, very rare at that price point. But with Oppo now discontinuing all their audio products I doubt I can get a review loaner from the company....

I just wanted to chime in and say the Pass HPA-1 is one of my two favorite solid-state headphone amps of all time (a title it shares with the Violectric V281, for different reasons). The HPA-1 seems strangely overlooked among headphone enthusiasts, and I'm not quite sure what to make of that. Perhaps it is too expensive for many yet "not expensive enough" for the rest? Who knows, the market is weird. All I know is the seemingly popular Simaudio 430HA has absolutely nothing on the Pass in my humble opinion.

Depending on who you talk to....other amps are better than those you like,which I'm sure is no surprise to you. I value your opinion, and have read some great recommendations from you,but that was on your picks on affordable headphones, such as the AKG K7XX, which I think we agree is a great value, and a good headphone for people who haven't bit into the land of diminishing returns.

What makes me really wonder though, is why not be at least a bit more objective in reviewing expensive gear by making blind comparisons between amps, and between expensive amps to those of lesser cost? What does that hurt? I sure can see what it would help.

I hear you on the affordable aspect. I try to cover less expensive amps whenever I find a good one worth recommending. So far I've placed the Arcam rHead ($599) on the Wall of Fame, and would have done the same with the Massdrop Cavalli CTH ($249) if it wasn't a limited run (which is just how Massdrop works). I am also extremely impressed with the Rupert Neve RNHP ($499) though I haven't actually written it up yet.

Any of those amps plus a K7XX and/or HD6XX, HE400i, etc, would make a really enjoyable combo. Not summit-fi performance, but the price/performance ratio would surely be more favorable.

As for comparisons, I will absolutely point out whenever a good-but-expensive amp is legitimately challenged by a more affordable option. That makes total sense to me.

Tyll and I don't agree on the Simaudio. I had one for a long time and just never got into it as a headphone amp. Not worth the price imho. I ended up using it more as a preamp in my speaker rig, where it did a wonderful job. So yes, we all hear and experience gear differently.

I heeded your advice and got the Cavalli Massdrop CTH. Again... your review was 100% right-on. I have a Schiit Jotunheim as well, and it has a ton going for it as well, especially in balanced mode. I wonder if there are other amps that run balanced, that are any better than the Jot, and of those, are there any that include a great DAC?

I like my Marantz HD-DAC1 more for it's DAC than it's headphone amp, though that is excellent too. I'm hearing more of what my CDs have now with my Focal Clear, and now notice and appreciate a better amp and DAC more than before.

So far the best sound I have is through a Marantz HDCD-1... toslink to the Marantz HD-DAC1, SE to the Jotunheim, running push-pull (balanced) out to the Focal Clear and Mr.Speakers AEON Flow Closed. That rig really also makes my Sennheiser HD600, and the AKG K7XX, and AKG 553 Pro closed sound more open and detailed and tight and deep in bass, smooth and more airy on top. The Cavalli CTH is wonderful too, with any headphone, straight out of the Marantx HDCD-1. I think I'm done now with my headphone quest, and thank you for all your advice John. I feel lucky to have found what I consider high value and great sound with your help.

Didn't see this until now. The differences are subtle but I find the Pass amp more incisive, detailed, and pure, while the Violectric is a bit more visceral and dynamic. That's an oversimplification but it will do the job.

Bob I’ve been a fan of your work as a recording engineer for decades and I must say you are among several of my favourite engineers .
I cobbled together a little headphone system consisting of the fabulous Mjölnir Audio Bipolar mk2 amplifier and Audeze LCD 4Z headphones, what a fantastic amplifier and what a fabulous headphone.
Easy to afford, very comfortable and a real thrill listening through and not to leave out my wife whom loves me even more especially when I switch over to using headphones.

Seems like the request for blind testing is a knee-jerk response from those that are disgruntled over the price tags of audio gear. I would think fair that if a reader requests a blind test then that reader should be blind to the price of these devices.

A lot of people don't seem to understand the huge initial costs shouldered by manufacturers in R&D, testing new materials, hardware tooling machinery, new components/parts/supplies procurement, training technicians to build them, voicing/listening tests, marketing, etc. that go into every new pair of headphones.

It's an extremely pricey undertaking to bring a new set of headphones (or any high-fidelity component) to market and be able to faithfully and consistently reproduce unit after unit with the same high standards of build and sound quality in every batch.

My hat is constantly doffed to the people who strive and work their asses off to bring new gear to market when half the people of the burning dumpster fires of online comments sections or forums (from the safe sidelines of their anonymity) will just bitch and moan about pretty much everything to do with anything headphone related that doesn't jive with their opinions or if it's new or priced more than $99.

A headphone is a complicated product with a staggering number of things that can get effed-up before parts even arrive to the manufacture for final build and QC if anything is being outsourced.

I love listening to music on headphones and I'll it'll be a cold day in hell before I'll let some online troll tell me how I should be doing it or with what gear I should be doing it with in order to actually enjoy myself.

Reading the comment pages can at times be as informative as the review, entertaining at the least which i would say many of these fall into the latter, that said, one can find a tidbit of useful info in most posts as i found here. As a PSAudio DSD to HPA-1 to LCD-X owner I find Mr Katz's #24 very informative as in "thank you for any and all ears" on a piece of gear and it's favored compatibility to related gear. If no demo gear is available one relies on recommendations from the highly reputable industry source guys like Drew Baird and Walter Underwood whose opinions can be considered biased even if you trust them, which I do. Mr Katz emphatically admitted in comments on #13 Headphone Shootout, he would not own Focal Utopias yet after that exhausting yet invaluable review the end user still wants to know how do the Utopias sound driven by the PASS HPA-1 ;) And ultimately the end user makes a choice based on reviews such as this one, which I personally find invaluable. Here's a secret many here might relate to, who among us really can afford this gear?,, I cannot and readily admit that I have made extreme sacrifices in order to fund the immense enjoyment this gear brings to my life. In that sense it is a very relative subject and I appreciate Mr Katz's approach in his esoteric way of observing and then sharing much like a Zen master sharing perception and wisdom along the path knowing one can only see clearly when finally one experiences it for himself. Having respect for another's opinion might just result in gained knowledge,, and how invaluable is that! Thanks Bob, i really appreciate your years and even more, your ears. Al Petrie @J1